Backside Illumination (BSI) image sensor chips are replacing front-side illumination sensor chips for their higher efficiency in capturing photons. In the formation of the BSI image sensor chips, image sensors and logic circuits are formed on a silicon substrate of a wafer, followed by the formation of an interconnect structure on a front side of the silicon substrate. The interconnect structure includes a plurality of metal layers. In the formation of the top metal layer in the plurality of metal layers, an Edge Bevel Removal (EBR) step may be performed to remove the metal that is deposited on the bevel of the BSI wafer. A passivation layer is then formed over the interconnect structure.
The formation of the image sensor chips involves one or more thin down processes to reduce the thickness of the semiconductor substrate on which the image sensors are formed. After thin down, the thickness of the semiconductor substrate is thin enough so that light can penetrate from the back surface of the semiconductor substrate. A trim process is also performed to trim some edge portions of the semiconductor substrate.